1. Field of the Invention
The present invention relates to an ink jet head and an ink jet printing apparatus having the head.
2. Description of the Related Art
According to a recording system using an ink jet head, heat energy or vibration energy is applied to ink to discharge the ink as fine droplets from nozzles to thereby form an image on a recording medium. An example of a method for manufacturing an ink jet head can be found in Japanese Patent Application Laid-open No. 2002-19120.
According to such a manufacturing method, an ink jet head is manufactured in the following manner. Initially, heat elements (discharge element part) and a wiring conductor for supplying electric power to the heat elements are formed on a silicon substrate, a protective film is formed on the wiring conductor, and ink passages and ink discharge ports are patterned using a resist.
Next, a material for nozzles is applied and cured, and holes for supplying the ink are opened in the silicon substrate from its backside to the discharge element part. The resist is then removed through the holes to thereby form the ink passages and discharge ports.
The silicon substrate is then cut into chips, each having a necessary size as a head, to yield head substrates. The head substrate is attached to a support plate made typically of alumina, and a plated layer or ball bump is formed on a pad for bonding a flexible wiring board. The flexible wiring board serves to supply electric power from outside of the head to the heat elements and other components. The flexible wiring board is then bonded to the resulting recording head.
Next, a sealant for sealing the periphery of the head substrate (chip) (hereinafter referred to as “chip-periphery sealant”) is applied to thereby protect the side of the head substrate from ink and dust. After curing the chip-periphery sealant, an inner lead bonding (ILB) sealant for sealing an electric splice (hereinafter referred to as “ILB sealant”) is then applied over the chip-periphery sealant.
The chip-periphery sealant for sealing the head substrate (chip) and the ILB sealant for sealing the electric splice must satisfy the following requirements.
The chip-periphery sealant must continuously flow, in a short time, in a narrow groove around the chip, having a width less than 1 mm, positioned at the boundary between the head substrate and the support plate supporting the head substrate. The chip-periphery sealant must also protect the chip (head substrate) from ink and other matter. The ILB sealant must completely seal the electric parts and must not peel off even when rubbed by a blade or wiper and even when paper jams and comes into contact with the sealed portion. The blade or wiper is placed in the printing apparatus and serves to clean the plane of the ink discharge ports on the top side of the head substrate. In addition, the ILB sealant must not contain components that adversely affect the ink-repellent function of the head face which is treated with, for example, an alkyl fluoride compound or low-molecular weight cyclic siloxane.
To satisfy the above-mentioned requirements, the chip-periphery sealant should preferably have low thixotropy, exhibit good flowability and be flexible over a wide range of temperatures. In contrast, the ILB sealant should preferably have high hardness, viscosity and thixotropy and maintain its shape.
In conventional techniques, an optimum material satisfying the requirements of the chip-periphery sealant, and one satisfying the requirements of the ILB sealant have been separately selected.
For example, a material comprising a flexible polybutadiene-modified epoxy resin and an amine curing agent is used for the chip-periphery sealant, and a “dam agent” (“dam material”) comprising a bisphenol-A epoxy resin, a curing agent and about 70% of an acid anhydride and filler is used for the ILB sealant.
However, these conventional techniques are susceptible to further improvement.
For example, if the ILB sealant is applied and cured after the chip-periphery sealant is applied and cured, it takes a long time to cure these two sealants, dedicated thermostats must be provided for curing the chip-periphery sealant and the ILB sealant, respectively, and spaces for the two thermostats are required, thus inviting higher cost of manufacture. An attempt has been made to shorten the curing time by applying a chip-periphery sealant, subsequently applying an ILB sealant, and performing curing treatment of these sealants in a certain period. However, the following problems have arisen.
In some cases, a thin uncured layer is formed at the boundary between the chip-periphery sealant and the ILB sealant, and the ink penetrates the uncured layer to thereby cause electrical failures. In addition, the ILB sealant contains a larger amount of filler, has a higher specific gravity and thereby sinks into the flexible chip-periphery sealant. Thus, the chip-periphery sealant flows over the chip, or cavities are formed in the cured sealants and ink penetrates the cavities.